Two-body wear of occlusal splint materials.

This study investigates the wear resistance of four different types of occlusal splint materials based on two-body wear simulations under wet and dry conditions. Twenty specimens of each splint material (Dentalon Plus, Orthoplast, Biocryl C, and Eclipse), each with a diameter of 16 mm and a thickness of 3 mm, were tested, half under wet and half under dry conditions. Each wear test was performed using a device called chewing simulator CS-4 (n=10; test load: 50 N; number of cycles: 10000, 20000, and 30000; continuous rinsing with 30°C water for wet conditions); the antagonists were simulated using steel balls. Wear was determined using a 3D laser scanner and a surface analysis program. To detect significant statistical differences, wear data after 10000; 20000; and 30000 cycles were compared using the Kruskal-Wallis test and the Mann-Whitney U-test. The level of significance was set at 5%. Significant differences were found between the groups of different materials tested under wet conditions (P<0.05), whereas no differences between them were found under dry conditions (P>0.05). No significant difference was found between the wet and dry conditions for all materials and cycles (P>0.05). For groups of different materials tested under wet conditions, the degree of volume loss generated in the Chewing Simulator CS-4 was found to differ significantly for different numbers of cycles. The presence of water had no effect on the volume loss in the different material groups that were tested.

The effect of occlusal contact localization on the stress distribution in complete maxillary denture.

The fracture of acrylic resin dentures is an unresolved problem in removable prosthodontics despite many efforts to determine its cause. Unfavourable occlusion could be playing an important role in the fracture of the denture. The aim of this study was to investigate the effect of occlusal contact localization on the stress distribution in complete maxillary denture bases utilizing two-dimensional finite element analysis. The results of this study have shown that maximum compressive stresses in a complete maxillary denture under functional masticatory forces concentrates always on the artificial tooth/denture base junction irrespective to the occlusal contact localization. Tensile stresses were observed in areas toward the midline, although the midline itself usually had lower stresses. Shifting the occlusal contacts to a more buccal localization resulted in an increase of the calculated stresses. As a conclusion, it can be speculated that the buccal placement of the occlusal contacts may play a role in the fatigue fracture of the complete maxillary denture.

Axial condyle morphology and horizontal condylar angle in patients with internal derangement compared to asymptomatic volunteers.

The purpose of this study was to evaluate the possible structural variations of axial condyle morphology and horizontal condylar angle between patients with internal derangement and asymptomatic volunteers. Forty-five symptomatic patients and 31 asymptomatic volunteers (AV) were included in this study. All subjects had bilateral high-resolution magnetic resonance imaging scans. Axial condyle morphology was evaluated using these images and classified into four diagnostic groups: convex, flat, and concave anterior surfaces, and tapered form. The angulation between the condylar long axis and the transversal plane was then measured. A Wilcoxon-Whitney-Mann-U-test demonstrated no significant differences in the horizontal angulation of the patients with disk displacement with reduction (DDR) (24.35+/-9.31) as compared to patients with displacement without reduction (DDN) (25.61+/-10.11) and asymptomatic volunteers (25.68+/-9.31) (AV). Eighty percent of the flat type condyles and 73.3% of the tapered type condyles belonged to the symptomatic patients with disk displacement with reduction (DDR) and without reduction (DDN). Chi-square test demonstrated significant differences between the diagnostic groups of condyle types (p<0.01). A comparison of the angular difference of right and left joints of asymptomatic volunteers and patients using the Wilcoxon-Whitney-Mann-U test showed that the results of the asymptomatic volunteers were significantly lower (p = 0.05). The conclusion that an increase in the horizontal condylar angle is a predisposing factor for the development of internal derangement or that the derangement develops during the prognosis of the disorder could not be clearly stated based on the results of this study. It is proposed that the difference between condyle morphology in patients with disk displacement and asymptomatic volunteers may be a result of the remodeling or degeneration caused by the disorder.

Morphology of the mandibular fossa and inclination of the articular eminence in patients with internal derangement and in symptom-free volunteers.

OBJECTIVE: The purpose of this study was to evaluate temporomandibular joint morphology and to compare possible structural variations in the temporomandibular joint anatomy of symptomatic anterior disk displacement patients with possible structural variations in the temporomandibular joint anatomy of symptom-free volunteers. STUDY DESIGN: Fifty-six symptomatic patients and 25 symptom-free volunteers were included in this study. All subjects had bilateral high-resolution magnetic resonance imaging scans performed in the sagittal (closed and open) positions. Disk positions were evaluated with these images, and the patients were accordingly classified into 4 diagnostic groups. The angulation between the Frankfort horizontal plane and the posterior slope of the articular eminence, as well as the width and depth of the glenoid fossa and the articular tuberculum, were automatically measured with the aid of a computer. RESULTS: The Mann-Whitney U test demonstrated significant differences in the angular and linear values obtained in disk displacement with reduction patients in comparison with the values obtained in patients with disk displacement without reduction and in symptom-free volunteers. CONCLUSION: It is proposed that a steeper posterior slope and higher tuberculum articulaire are predisposing factors for the development of disk displacement with reduction. Flattening of the eminence may progress in time, leading to the onset of disk displacement without reduction.

Evaluation of the slope of the articular eminence and the transverse angle of the glenoid fossa in an Anatolian population.

The purpose of this study was to compare a computer-aided method specially programmed for the measurement of the posterior angle of the articular eminence with formerly used methods, to investigate the angulation differences at different depths of slices, and to evaluate correlation with the transverse angulation. Three slices (central, medial, and lateral) at various depths of the glenoid fossa belonging to 64 dry skulls and two measurement methods were used in this study. The angulation of the articular eminence were measured and the transverse angle of each fossa calculated. No statistical difference was found between the articular eminence results of the two methods. According to the results, the one factor ANOVA central slice was found to be statistically steeper than the other two slices (p < 0.05) (central = 60.33 +/- 10.19, medial = 58.26 +/- 8.6, lateral 58.28 +/- 10.1). No correlation was found between the transverse angle of the inclination of the posterior slope angulation. It was concluded that the computer-aided method is more reliable and accurate and is much easier to use when compared to the manual method. An additional important finding of this study is that the inclination of the articular eminence should be evaluated at various depths of the temporomandibular joint.